hedgezzz的部落格

從這裡來的文章 :

http://my.safaribooksonline.com/book/programming/cplusplus/9780321545183/associative-containers/ch03lev1sec6

sample :

template< typename MapType, // type of map
          typename KeyArgType, // type of Key
          typename ValueArgtype> // type of Value
typename MapType::iterator efficientAddOrUpdate(MapType& m,
                                                const KeyArgType& k,
                                                const ValueArgtype& v)
{
    //find where k is or should be
    typename MapType::iterator Ib = m.lower_bound(k);
    if ( Ib != m.end() && // if Ib points to a pair
         !(m.key_comp()(k, Ib->first)))
    {   // whose key is equivalent to k...
        Ib->second = v; // update the pair's value
        return Ib; // and return an iterator to that pair
    }else {
        typedef typename MapType::value_type MVT;
        // add pair(k, v) to m and return an iterator
        // to the new map element
        return m.insert(Ib, MVT(k, v));
    }
}

int main()
{

    map<int,int> m1 ;
    for(int idx=0;idx<10;idx++)
    {
        pair<map<int,int>::iterator,bool> px  ;
        px =  m1.insert(std::map<int,int>::value_type(idx,idx)) ;
        if(px.second == false)
        {
            cout << "1:"<< idx << " existed,val=" << px.first->second << endl ;
        }
        px = m1.insert(std::map<int,int>::value_type(idx,idx*idx)) ;
        if(px.second == false)
        {
            cout << "2:"<< idx << " existed,val=" << px.first->second << endl ;
        }
    }
    for(int idx=0;idx<10;idx++)
        cout << m1[idx] << " " ;
    cout << endl ;

    map<int,int> m2 ;
    for(int idx=0;idx<10;idx++)
    {
        efficientAddOrUpdate(m2,idx,idx) ;
        efficientAddOrUpdate(m2,idx,idx*idx) ;
    }
    for(int idx=0;idx<10;idx++)
        cout << m2[idx] << " " ;
    cout << endl ;

}

2:0 existed,val=0
2:1 existed,val=1
2:2 existed,val=2
2:3 existed,val=3
2:4 existed,val=4
2:5 existed,val=5
2:6 existed,val=6
2:7 existed,val=7
2:8 existed,val=8
2:9 existed,val=9
0 1 2 3 4 5 6 7 8 9
0 1 4 9 16 25 36 49 64 81